For the N = 50-56 zirconium (Z = 40) and molybdenum (Z = 42) isotopes, the evolution of subshells is evaluated by extracting the effective single-particle energies from available particle-transfer data. The extracted systematic evolution of neutron subshells and the systematics of the excitation energy of the octupole phonons provide evidence for type-II shape coexistence in the Zr isotopes. Employing a simplistic approach, the relative effective single-particle energies are used to estimate whether the formation of low-lying octupole-isovector excitations is possible at the proposed energies. The results raise doubts about this assignment.
Gregor, E. T., Scheck, M., Chapman, R., Gaffney, L. P., Keatings, J., Mashtakov, K. R., O'Donnell, D., Smith, J. F., Spagnoletti, P., Thuerauf, M., Werner, V., & Wiseman, C. (2017). Shell evolution of stable N=50-56 Zr and Mo nuclei with respect to low-lying octupole excitations. European Physical Journal A, 53, . https://doi.org/10.1140/epja/i2017-12224-7